A printer including a recording head configured to eject ink supplied from an ink cartridge through nozzles is known in the art. For example, Japanese Patent Application Publication No. HEI 6-15834 discloses an ink cartridge formed with an ink supply hole for supplying ink to a recording head. A seal rubber is attached to the ink supply hole for preventing leakage of ink. Further, a cap for fixing the seal rubber to the ink supply hole is also attached to the ink supply hole. The cap is capable of being attached to the ink supply hole by a snap-fitting. Accordingly, detachment of the cap is restrained.